The present invention relates to an apparatus for the production molding of a multi-component plastic, especially polyurethane. The molding apparatus includes a stand and two mold parts affixed to mold holders in the stand. These mold parts can be brought by movement of at least one of the mold holders to a first position in which the parts are a small distance apart. The mold holders have back surfaces extending substantially transversely to the direction of the closing movement. The molding apparatus further includes a propping system, provided on the sides of the mold holders that face away from the mold parts, which is movably mounted on the stand. The propping system has propping elements which in the first position can be brought into engagement with the back surfaces of the mold holders. Finally, the molding apparatus includes a jacking system on at least one mold holder by which the mold parts can be brought closer together and jacked into a second position with the propping system engaged.
Molding apparatus of the type described above is disclosed in the Swiss Patent No. 377,094. It serves for the production of moldings from thermoplastics. The jacking system in this apparatus consists of a press piston of large diameter which can be displaced in the one mold holder and which, in turn, encloses an auxiliary piston of small diameter held in the stand and having a coaxial working cylinder. The mold holder described is thus movable with respect to the other mold holder, which makes it possible to bring the two mold parts up to a small distance apart by energizing the auxiliary piston. They are held in this position by abutments which, when the working cylinder is extended, are deployed from two slots that are situated opposite one another and reach below the bottom of the working cylinder. The auxiliary piston is thus not under hydraulic pressure during the subsequent delivery of pressure to the pressing piston, which permits the achievement of great closing pressure in the mold. The relatively movable mold holder, however, has a great inertial mass as a result of the inclusion of the pressing piston and working cylinder in its weight, and this militates against the achievement of short cycling times during normal operation.
Another molding apparatus of this type is disclosed in the U.S. Pat. No. 3,816,044. In the closed position, in which the mold parts are at a short distance from one another, the two mold holders are propped by locking closures that are mounted in the stand and are at an invariable distance apart. The masses that are moved in the opening and closing of the mold, however, are also very great.
Still another molding apparatus of this type is disclosed in German Utility Model Patent No. 84 17 747. The closing movement and propping function in this device are performed by a piston-and-cylinder unit which introduces the necessary forces through punctiform node points into both mold holders. The mold holders and the piston-and-cylinder units must be made correspondingly sturdy and, on account of this great weight, relatively high acceleration forces are produced during rapid opening and closing actions, making it difficult to sensitively control the closing force. The use of complex control and auxiliary units for the achievement of satisfactory performance is indispensible in this device.